Method for forming fluoroplastic articles

ABSTRACT

The present invention relates to a method for forming fluoroplastic article, comprising inner and outer fluoroplastic layers and a metal meshwork, the metal meshwork being arranged between the inner and outer fluoroplastic layers, characterized by the meshwork can be stretched and compressed in the axial direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/501,152, filed Aug. 7, 2006 which claims the priority of ChinesePatent Application No. 200610023720.5, filed Jan. 25, 2006, the entirecontent of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a fluoroplastic article, particularlyto a fluoroplastic article with liner made of metal meshwork.

DESCRIPTION OF THE RELATED ART

It has well known that fluoroplastic, particularlypolytetrafluoroethylene plastic (briefly to say, F4 or PTFE) is used asliners of steel members such as anticorrosive tubes, towers and vessels.When an article made of F4 is used as liners of a steel member, due to ahigh difference of thermal coefficient of expansion between the articleand the steel member, usually they will be destroyed during using. Thus,it has restricted the wide use of this new material in anticorrosivefields. Therefore, the inventor has proposed a F4 liner with metal weblaid in it, such that the excessive expansion of the anticorrosivearticle made of F4 gets restricted during being heated, so as toincrease the life of the F4 liner. But the grids of the metal web in theabove solution are invariable square one, that is, the wire of the webis fixedly connected with each other, so the metal web can't bestretched and compressed optionally, as shown in FIG. 1. There are twoshortcomings existing in the web with this structure. 1) Since the gridsof the metal web can't be stretched and compressed, when thefluoroplastic article is placed into a tube for example and is expandedto be flanged at the two ends, the metal web in the fluoroplasticarticle can't be flanged together with the fluoroplastic layer. Thus,the quality and performance of the fluoroplastic article aredeteriorated. 2) In the winding process during producing thefluoroplastic article, the metal web with above structure can merely belaid outside of the fluoroplastic belt, but can't be made into meshworkand placed in the fluoroplastic layers. Because the diameter of themeshwork with this structure is not stretchable and compressibleoptionally and the meshwork is difficult to abut against thefluoroplastic inner layer closely, when the fluoroplastic belt iswinding outside of the inner layer, the web will distort. When thearticle is sintered at a high temperature, since the F4 belt, metal weband glass belt can't be pressed against each other closely, the innerpressure due to the expansion is insufficient, and the metal web willdisorder and displace. Thus, the finished articles will have a lowdensity and there will be small holes in the structure. At the sametime, these articles will have a trend to crack and will have a highratio of defective and waste products.

SUMMARY OF THE INVENTION

The problem to be solved of the present invention is to provide afluoroplastic article with a liner made of metal meshwork. It canovercome above shortcomings arising in prior fluoroplastic articles,whose liners are made of metal web with fixed grids.

The fluoroplastic article according to the invention is composed ofinner and outer fluoroplastic layers and a metal meshwork. The metalmeshwork arranged between the inner and outer fluoroplastic layers canbe stretched and compressed in the axial direction.

In order to stretch and compress metal meshwork in the axial direction,the grids of the metal meshwork have variable rhombic shape. They areformed by interweaving metal wires or through welding metal webs withstretchable and compressible rhombic grids.

The advantage of the invention is set forth in the following. 1) Sincethe metal meshwork is stretchable and compressible, it can be compressedaccording to the diameter of the inner layer of the wound fluoroplasticarticle. As the result of being compressed, the diameter of the meshworkextends to be larger than that of the inner layer of the fluoroplasticarticle. Then, the inner layer of the fluoroplastic article is sheathedby the compressed meshwork. The latter is stretched and the diametergets small. In this way, the meshwork abuts against the outside of theinner layer. Next, the fluoroplastic outer layer is wound around themeshwork continuously. During winding, the grids of the metal meshworkvary with the state of winding and forces. Thus, the metal meshwork isarranged between the inner and outer layer of the fluoroplastic articlesubmissively, neatly, normally and uniformly without any disorders anddisplacements. Thereby, both quality and yield of articles are improved.2) Since the diameter of the meshwork is variable, when thefluoroplastic article with the metal meshwork is lined in a metalmember, the metal meshwork can be flanged together with thefluoroplastic layer. Therefore, both quality and performance of themember are improved. 3) As the force applied to different parts of themeshwork is uniform, the article doesn't deform at a high temperature.4) Since the product of the diameter and the length of the meshwork is aconstant, during producing and using, the meshwork will elongatelongitudinally and the diameter will expand in the transverse directionwith the rise of temperature. Since the tendency to elongatelongitudinally and the tendency to expand transversely are restrictedwith each other, both the length and the diameter of the meshwork can'tchange. Thus, the performance of expanding with heat and contractingwith cold of the article is in an optimum state. 5) Since the metalmeshwork of the article is stretchable, during winding or being sinteredat high temperature, the meshwork never displaces and will abut againstinner and outer fluoroplastic layers closely. Thus, the problem arisingby metal web with invariable grids is dissolved absolutely, and thesintered article has a high density and strength, and a good quality anda high success ratio as well. Meanwhile, the finished article whosesurface is smooth also has no blowholes or cracks.

Detailed description of exemplary embodiments will be described inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the square web with fixed grids, which isused in prior fluoroplastic articles.

FIG. 2 is a schematic view of the metal meshwork according to theinvention, which has variable rhombic grids.

FIG. 3 is a schematic view of the metal meshwork in FIG. 2, which is inthe compressed state.

FIG. 4 is a schematic view of the metal meshwork in FIG. 2, which is inthe stretched state.

FIG. 5 is a schematic view of the change of metal meshwork according tothe invention in the flanged portion, this portion is formed by themetal meshwork engaged with a tube.

FIG. 6 is an section view taken from arrow A-A in FIG. 5.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The embodiment shown in FIG. 2, FIG. 5 and FIG. 6 is a fluoroplasticarticle with a metal meshwork. It is used as liners of metal tubes andcomposed of inner and outer fluoroplastic layers 1 and a metal meshwork2. The metal meshwork 2 is arranged between the inner and outerfluoroplastic layers. The grids 3 of the metal meshwork 2 have variablerhombic shape and can be formed by interweaving metal wires. They alsocan be made through welding metal webs with stretchable and compressiblerhombic grids. The metal meshwork with such a configuration can bestretched and compressed in the axial direction.

The above fluoroplastic articles with metal meshwork can be made byfollowing processes: (1) A thin fluoroplastic (e.g. F4) belt is woundaround a stainless steel mold back and forth until the desired thicknessreaches, so as to make the inner layer of the article; (2) The metalmeshwork which is compressible in the axial direction is compressed, sothat the diameter of the meshwork is larger than that of thefluoroplastic inner layer. Then, the fluoroplastic inner layer issheathed by the compressed meshwork. The latter is stretched and thediameter of it gets small. As the result, the meshwork abuts against thefluoroplastic inner layer closely; (3) The thin fluoroplastic belt iswound around the metal meshwork until the desired thickness reaches, soas to make the outer layer of the article; (4) The outer layer isclosely strapped by a glass belt; (5) The strapped fluoroplasticprefabricated article is placed into an oven. The article is finishedafter being sintered in the oven. The temperature of the sintering ovenmay be set according to the different composition of the fluoroplastic.When F4 plastic is used, The temperature of the oven is about 380° C.

1. A method for producing a fluoroplastic article, having inner and outer fluoroplastic layers and a metal meshwork, the metal meshwork being between the inner and outer fluoroplastic layers, and wherein said meshwork is stretchable and compressible in the axial direction, comprising: (1) winding a thin fluoroplastic belt around a stainless steel mold back and forth until the desired thickness is reached, so as to make an inner layer of the article; (2) compressing the metal meshwork in axial direction, so that the diameter of it is larger than that of the fluoroplastic inner layer, after the fluoroplastic inner layer is sheathed by the compressed meshwork, the latter is stretched and the diameter is made smaller, such that the meshwork closely abuts against the fluoroplastic inner layer; (3) winding the thin fluoroplastic belt around the metal meshwork until the desired thickness is reached, so as to make the outer layer of the article; (4) closely strapping the outer layer with a glass belt; (5) placing and sintering the strapped fluoroplastic article in an oven where it is to form the finished article. 